Chemical heat pump

ABSTRACT

A chemical heat pump system is disclosed for use in heating and cooling structures such as residences or commercial buildings. The system is particularly adapted to utilizing solar energy, but also increases the efficiency of other forms of thermal energy when solar energy is not available. When solar energy is not available for relatively short periods of time, the heat storage capacity of the chemical heat pump is utilized to heat the structure, as during nighttime hours. The design also permits home heating from solar energy when the sun is shining. The entire system may be conveniently rooftop located. In order to facilitate intallation on existing structures, the absorber and vaporizer portions of the system may each be designed as flat, thin wall, thin pan vessels which materially increase the surface area available for heat transfer. In addition, this thin, flat configuration of the absorber and its thin walled (and therefore relatively flexible) construction permits substantial expansion and contraction of the absorber material during vaporization and absorption without generating voids which would interfere with heat transfer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a division of my copending application Ser. No. 135,726, filedMar. 31, 1980, now abandoned, which was a division of my applicationSer. No. 958,507 filed Nov. 7, 1978, now U.S. Pat. No. 4,224,803, issuedSep. 30, 1980, which was a continuation-in-part of my application Ser.No. 842,702 filed Oct. 17, 1977, now U.S. Pat. No. 4,272,268, whichissued June 9, 1981.

BACKGROUND OF THE INVENTION

This invention relates to heat pumps and, more particularly, to the useof chemical heat pumps for converting and storing solar energy, makingsolar energy a practical source for heating and cooling residential orcommercial structures. It also relates to the solar collector used withthe heat pump.

Absorption refrigeration systems for the purpose of storing thermalenergy are known. My prior U.S. Pat. No. 3,642,059, issued Feb. 15,1972, shows a particularly efficient small-scale absorption system usedfor refrigeration purposes and also for heating purposes on a storedenergy basis. This system has not, however, in the past been designed inthe form required for converting and storing solar energy forlarge-scale space heating or other purposes. In addition, these systemshave not been used as combination heat pumps and heat storage systems,which are periodically regenerated to effectively apply cyclicallyavailable solar energy for such heating applications. Space heating, ofcourse, requires substantial energy levels to be produced over extendedperiods of time. In addition, the space heating problem is cyclic,generally occurring on a 24-hour cycle, which requires daily use and mayrequire daily regeneration of the heat pump system.

Prior absorption refrigeration systems have not been designed whichwould satisfactorily operate to store and convert energy in thisenvironment. One of the more important factors limiting theeffectiveness of prior systems based on powdered absorbants has been thefact that, because of the low vapor pressures within the containersgenerally required for their satisfactory operation, the containers havegenerally been built as relatively heavy and expensive rigid structures.During absorption and desorption, the vapor-absorbant powder expands andcontracts physically. This size change (particularly after numerouscycles of absorption and desorption), tends to lift the chemical fromthe container walls and to produce voids within the powder bed. Sincethe container walls are used for the purpose of heat transfer, theseresulting evacuated voids between the chemical and the container walland throughout the powder significantly reduce the effectiveness of thesystem.

Solar systems in the past, particularly those which use flat platecollectors without concentrators (and especially those in which the flatplate collector is left at a single orientation year around), havesuffered from substantial heat losses to the environment, even thoughone or more layers of transparent material were used to cover theabsorbing surface. Normally, in such systems the layers of air betweenthe transparent plates have been static. The static air present betweenthe transparent layers in prior systems has, through convection,conducted heat to the ambient which significantly reduces the overallefficiency of the solar collection system.

The usual method considered in prior systems of storing solar energy foruse during nighttime hours has been either through the sensible heat ofwater or other material, with satisfactory heat capacity or through theheat of fusion of salts. The prior systems require substantial size andweight, and usually are not feasible for rooftop installation. Priorsimilar solar systems have not incorporated a heat pump which permitsthe utilization of heat extracted from the atmosphere to enhance theefficiency of alternate heat sources, such as fossil fuel sources, whichmust be used during periods of extended cloudiness.

SUMMARY OF THE INVENTION

The present invention alleviates these and many other difficultiesinherent in prior art space heating systems by utilizing a chemical heatpump which may be adapted to be roof mounted. The system utilizes, inthe preferred embodiment, a combination of water as an evaporatingliquid and a solid magnesium chloride hydrate or a lithium chloridehydrate as a water vapor-absorptive chemical. The water and theabsorbant are stored in separate containers in a heat-exchangerelationship with the space to be heated or cooled, the externalatmosphere, or a secondary heat source such as a fossil fuel combustor.The container housing the vapor absorptive chemical is preferablypositioned on the rooftop for direct collection of solar energy. Thevaporizer container, storing the liquid to be vaporized, is preferablymounted on a rooftop location either in the shade of the absorber orwithin the roof structure, but, at any rate, out of the direct path ofthe sun's rays. These two containers are connected to one another by aconduit which permits vapor to pass through during evaporation ordesorption in one container while absorption or condensation occurs inthe other container during any one of the various operational modes ofthe system.

The heat exchanger utilizes air ducts connected to air spacessurrounding the containers. Theses ducts are valved in a manner whichpermits, through the simple manipulation of a minimum number of controlvalves or dampers, the operation and regeneration of the system duringthe various seasons and during daytime and nighttime operation.

The containers housing the vapor absorptive chemical and the liquid tobe vaporized are both critical in their construction, since each must becapable of very substantial heat transfer to the heat exchanger airspaces as well as very substantial vapor transfer from one container toanother during use and regeneration and each must be made of inexpensivematerials. A preferred embodiment of the present invention utilizesthin, large, flat pans for each of these containers, the pans includinginternal structural support members to support the external atmosphericload on the containers. The vapor absorptive chemical is preferablystored along one surface of the flat absorptive chemical container, thisbeing the surface which is subjected to solar radiation. The chemicalmay be maintained against this surface by a corrugated or zig-zagged,vapor permeable partition, this zig-zagging substantially increasing thesurface area for vapor flow. It has also been found that the surface ofthe vapor absorptive chemical container subjected to solar radiation maybe identically corrugated or zig-zagged so that the heat transfersurface area, as well as the solar absorption surface area, may beincreased. The overall effect of this corrugation has been tosubstantially increase the heat and vapor transfer characteristics ofthe system without requiring increased quantities of vapor absorptivechemical. However, in some cases this zig-zag structure is not needed.

In addition, very thin metal is used to form the vapor absorptivechemical container, allowing the walls to flex. Due to the higherpressure outside the container, this flexing tends to prevent voidsfrom: forming due to expansion and contraction of the chemical, andassuring substantial, long-term, efficient operation.

The solar-radiation absorbing surface of the vapor absorptive chemicalcontainer is preferably separated from the ambient atmosphere by one ormore layers of transparent material, such as glass. The space betweenthe container and the first such glass layer forms a part of the heatexchanger mentioned previously, and air used for heat transfer purposesis pumped through this space at a carefully selected velocity Thisvelocity assures that the air flow remains stable and substantiallywithout eddies. While air flow of this type reduces the effectivetransfer of heat from the container to the flowing air, this effect isnot critical due to the design of the absorber which has a relativelylarge surface area. Of more importance, it has been found tosubstantially reduce the heat loss by convection from the chemicalcontainer to the atmosphere, thus increasing the overall collectorefficiency of the system by utilizing the air flow also required forhome heating.

The present invention provides an extremely efficient absorption heatpump for space heating particularly adapted to solar energy wherein theheat pump may be used to both heat and cool the house in the winter andsummer months, respectively . and may also be used for reducing thethermal energy input required during fossil fuel or other alternateenergy source heating of the structure during very extended sunlessperiods by utilizing energy from the ambient surroundings to enhance theheat input of such alternate heat source systems.

These and other advantages of the present invention are best understoodthrough the following detailed description of a preferred embodimentwhich references the drawings, in which:

FIG. 1 is a chart illustrating the vapor pressure-temperaturerelationship for a water-magnesium chloride tetrahydrate system;

FIG. 2 is a schematic sectional view showing a residence or otherstructure with the chemical heat pump of the present inventioninstalled;

FIG. 3 is a perspective view of the heat pump system of FIG. 2 showingthe duct work and valving system for controlling the operation of thissystem;

FIG. 4 is an exploded perspective view of the vaporizer containers ofthe present invention and their interconnection with the heat transferduct;

FIG. 5 is a longitudinal sectional view of the vaporizer container ofFIG. 4 showing its interconnection with the heat transfer duct and thevapor droplet trap used in the vapor conduit;

FIG. 6 is a partially broken away plan view of the evaporator containerof FIGS. 4 and 5 showing the various layers of the container and itsconstruction;

FIG. 7 is a sectional view of the vapor absorptive chemical tray of thepresent invention, along with its mounting hardware and transparentcover used for limiting convection losses to the atmosphere ambient;

FIG. 8 is a plan view, partially broken away, showing the various layersin the vapor absorptive chemical solar collector of FIG. 7;

FIG. 9 is a sectional view taken along lines 9--9 of FIG. 3 at rightangles to the sectional view of FIG. 7 showing the interconnection ofthe vapor absorptive chemical tray to the heat transfer duct of thesystem;

FIG. 10 is a perspective view, partially broken away, of an alternateembodiment absorber panel for use with the present invention, theabsorber panel of this embodiment forming a more efficient solarcollector;

FIG. 11 is a sectional view of the solar collector of FIG. 10 showingcertain structural details thereof;

FIG. 12 is a sectional view of an improved embodiment of the absorberpanel of FIG. 10 for use with the present invention, the absorber panelof this embodiment forming a more efficient and inexpensive solarcollector;

FIG. 13 is a sectional view of the absorber panel of FIG. 12 taken alonglines 13--13;

FIG. 14 is a perspective view, partially broken away, of an alternatevaporizer container for use with the present invention, the vaporizercontainer of this embodiment forming a more durable and inexpensivevaporizer container;

FIG. 15 is a cross-sectional view of the vaporizer container of FIG. 14taken along lines 15.15; and

FIG. 16 is a schematic sectional view showing a residence or otherstructure with the chemical heat pump of the present inventioninstalled, similar to the view of FIG. 2, while showing instead anembodiment useful for heating the structure for very low outsidetemperatures.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Prior to a description of the system hardware, it is helpful tounderstand, in detail, the chemical processes which occur in the solarheat pump of the present invention. In this regard, initial attention isdrawn to FIG. 1 which is a vapor pressure-temperature illustration for awater-magnesium chloride system, and, in particular, for awater-magnesium chloride tetrahydrate/dihydrate system.

In the chemical heat pump, water and the absorptive chemical are storedin separate containers and maintained at different temperatures, with aconduit between the two so that water vapor can flow from one containerto the other. This aspect of the operation of the system is identical tothat described in my U.S. Pat. No. 3,642,059, which I incorporatedherein by reference. Water vapor thus flows between the two containersin response to any vapor pressure differential therebetween. In thediagram of FIG. 1, the line 13 shows the vapor pressure-temperaturerelationship of water at its transition from a solid or liquid to a gas.The line 15 shows the corresponding vapor pressure-temperatureinterrelationship for the transition defined by the equation MgCl₂ ·4H₂O(s)=MgCl₂ ·2H₂ O(s)+2H₂ O(g). It will be seen that the temperature oftransition for the solid or liquid water for a given vapor pressure andthe temperature for transition of the magnesium chloride hydrate areapproximately 150° apart at most pressures. It will likewise be notedthat the temperature differential between the materials is approximately130° when the vapor pressure of water at transition is at a firstpressure and the vapor pressure of the magnesium tetrahydrate attransition is at one-half this first pressure.

As previously described, water in solid or liquid form is housed in afirst container and magnesium chloride dihydrate is housed in a secondcontainer. The following description assures that either of the firstand second containers can alternately be connected to the structure tobe heated or cooled, or to the outside ambient atmosphere. In addition,the absorptive chemical container may be heated by solar energy or analternate energy source, such as a fossil fuel.

Cooling or refrigerating the structure while liberating heat to theatmosphere, is accomplished as a two-stage process. In the first stage,the water container, or vaporizer, is maintained, for example, at apoint 17 in FIG. 1 where it evaporates and provides cooling by heattransfer between air pumped or blown from the structure to be cooled. Ascan be seen, the vaporizer container in this example, is atapproximately 32° F. and sublimation of the enclosed ice withdraws 21.04KCal heat of vaporization per gram mole, plus 2.87 KCal heat of fusion,for a total of 23.91 KCal per gram mole. Simultaneously, at point 19,the vapor absorptive chemical container is in a heat transferrelationship with the external environment and liberates heat to theenvironment at approximately 145° F. It is also in vapor transferrelationship with the vaporizer. The heat liberated at point 19 in thefigure is equal to 32.41 KCal heat of absorption, less 0.97 KCalsensible heat to warm the vapor, or 31.44 KCal per gram mole which isdissipated to the environment at 145° F. This heat may be carried to theenvironment by air pumped around the chemical tray and then exhausted.It will be seen from the figure that point 19 is at a pressure ofapproximately one-half the pressure at point 17, so that the evaporatedvapor self-pumps within the system, leaving the evaporator container atpoint 17 and being absorbed at the vapor absorptive chemical containerat point 19. This two-to-one relationship is chosen as an example, andrelationships approaching unity are also satisfactory.

In the second stage of the refrigeration process, the system isregenerated by heating the tetrahydrate to 225° as shown at point 21,utilizing either solar energy directly absorbed by the vapor absorptivechemical container or alternate energy sources such as fossil fuels. Theenergy required must be sufficient to provide sensible heat of 3.75 KCalper gram mole to warm the tetrahydrate to 225° F, and then 32.41 KCal todesorb the two moles of water vapor at point 21 conditions, for a totalof 36.16 KCal per gram mole. The desorbed water vapor spontaneouslytransfers to the original vaporizer and condenses to liquid at point 23conditions at 75° F. Here 21.04 KCal heat of vaporization plus 0.60 KCalsensible heat for a total of 21.64 KCal per gram mole is liberated tothe surroundings by heat transfer to a flow of ambient air. Further,cooling the original vaporizer to 32° F. to again begin the first stageof the cycle requires about 0.86 KCal plus 0.37 KCal sensible heats forthe dihydrate and vapors, respectively, and a further 2.87 KCal tofreeze the water for a total of 4.1 KCal. This is taken from the 23.91KCal cooling provided as previously described at point 17, to leave afinal cooling effect of 19.81 KCal per gram mole at 32° F. This resultsin a coefficient of performance of 0.55 KCal cooling per KCal heatinput. As previously mentioned, during sunny days this heat input may beprovided by solar radiation. On cloudy days, it may be provided by analternate energy source, although the latter should not often berequired when air conditioning is needed in the structure.

When the system is to be used in a heating mode, the chemical heat pumpcan significantly increase the effective output of a thermal source byextracting additional heat from the ambient surroundings. Such heatingis a two-stage, continuous process. The first stage of heating isidentical with the cooling stage. In this case, however, the vaporizeris located in a heat exchange relationship with the external environmentwhich is assumed to be at 32° F. in FIG. 1, or point 17. It withdraws,on vaporization, thermal energy equivalent to the heat of vaporizationof the enclosed water from the atmosphere. At the same time, theabsorber is at point 19 in FIG. 1 and is located in a heat exchangerelationship with the house being warmed where it liberates the heat ofvapor absorption at approximately 145° F. During the second heatingstage, the original vaporizer is placed in a heat exchange relationshipwith the area being heated while the original absorber is heated by athermal source, such as a gas flame or solar energy. The absorber isthereby raised in temperature to approximately 290° at point 25 in FIG.1 so that the vapor pressure of the enclosed vapor absorptive chemicalexceeds the vapor pressure in the vaporizer container when it is at atemperature, as needed for warming, such as the temperature 145° F. atpoint 27 of FIG. 1. Thus, during this second stage of the heating cycle,vapors desorb from the original vapor absorptive chemical and movethrough the vapor conduit to the original vaporizer container, and therecondense to liberate heat of condensation at a temperature required forheating.

During this heating cycle, the vapor pressure ratio between the absorberand vaporizer containers during each operating mode is maintained atapproximately 2 to assure adequate vapor flow. This same ratio will benoted in the case of the refrigeration cycle but, as indicatedpreviously, ratios approaching unity are also satisfactory. Beginning atpoint 17, 21.04 plus 2.87 KCal thermal energy is removed from thesurroundings by sublimation of ice at 32° F. Simultaneously at point 19,31.44 KCal is provided at 145° F. to the area being heated. Next, thehydrated absorber is externally heated from 145° F. to 290° F. to raiseit from point 19 to point 25 in FIG. 1, which requires 4.6 KCal sensibleheat addition. This is followed by addition of 32.41 KCal to desorbwater for a total of 37.03 KCal per gram mole. During this desorption,21.05 KCal heat of condensation plus 1.07 KCal sensible heat fromcooling water vapor from 290° F. to 145° F., or 22.1 KCal per gram moleis liberated for heating purposes at point 27 by the original vaporizer.The dehydrated absorber is subsequently placed in a heat exchangerelationship with the area being warmed and returns 3.13 KCal sensibleheat on cooling from 290° F. to 145° F. Finally, the vaporizer containeris cooled by heat exchange with a 32° F. external environment and thecycle is complete. The overall heat supplied by the absorber andvaporizer at 145° F. or higher is 56.69 KCal per gram mole, while thetotal thermal energy taken from the external heater at point 25 is 37.03KCal per gram mole. This results in a coefficient of performance of 1.53thermal units output for each thermal input from the heater. The extraenergy is supplied by the 32° F. environment cooperating with the heatpump for temperature increase.

Solar energy, as is well known, requires the storage of very largequantities of heat. The heat pump of the present invention stores morethermal energy than any known practical device for a given quantity ofmaterial and delivers this energy, on demand, even after the storagetemperature has fallen. Furthermore, the storage is capable of lastingindefinitely so that, for example, heat can be accumulated over a periodof several days and later supplied over a period of several days, as isrequired in some instances for a truly effective solar energy system forspace heating.

Referring again to FIG. 1, the use of this heat pump for energy storageis best uncerstood through a reexamination of the simultaneous operationof the system at points 21 and 23. During this operation, 32.41 KCal issupplied at 225° F. at point 21 while 21.04 KCal is dissipated at anambient temperature of 75° F. to the environment. The energy 32.41 KCalis stored in the system. To liberate this energy, the absorber is placedin a heat exchange relationship with the area to be warmed, as at point29 of FIG. 1, while the vaporizer is exposed to heat exchange with theambient environment at point 23, where ambient air is utilized tomaintain its temperature at 75° F. On initiation, 21.04 KCal iswithdrawn from the environment and the original 32.41 KCal is providedby the absorber at the higher temperature. This energy outputcorresponds to 349 btu per pound of total chemicals. This, of course, isan extraordinary energy storage capacity supplied by the system whichmakes it particularly advantageous in solar applications. Othertemperatures for the vaporizer and absorber are also satisfactory,depending on the relationships of FIG. 1.

It should also be noted that this invention is not restricted tolocating the vaporizer in heat exchange relationship with the externalatmosphere only during this first heating stage. It is also contemplatedthat, for very cold outside air temperatures, the vaporizer may belocated in heat exchange relationship with the ground or with air fromthe interior of the structure being heated. In the latter case, suchair, which is normally heated by contact with the absorber, is firstpassed over the vaporizer. The heat exchanged into the air of thestructure to be heated in this latter case is necessarily reduced by theheat of vaporization lost to the vaporizer, 21.04 KCal per mole. Thus,neglecting the gain or loss of sensible heat, the heat exchanged to theinterior air of the structure to be heated is 32.41 KCal per mole heatof absorption minus 21.04 KCal heat of vaporization, which results in11.37 KCal per mole or 122 Btu per pound of total chemicals. Althoughthis represents a significant reduction from 349 Btu in the amount ofthe heat output by the absorber to the interior air, it is still higherthan competitive systems. Further, passing the interior air over thevaporizer is desirable when the outside temperatures are so low that thechemical heat pump of this invention would not otherwise operateefficiently to heat the interior of the structure.

It will be recognized again that, during this heating operation, thethermal energy required to raise the vapor absorptive chemical containerat point 25 of FIG. 1 to 290° F. may be supplied by solar energy.

It can be seen, therefore, from FIG. 1 that the heat pump system of thepresent invention is advantageous for refrigerating and heating theinterior of a structure using heat pump processes, as well as forstoring energy, which makes it particularly adaptable to solar energyheating and cooling. It will also be recognized that the present systemis particularly applicable to any thermal energy source which is subjectto cyclic variations, such as may be derived from wind or tidal energy.

It will also be seen that the system utilizes (a) selective heatexchange between the vaporizer and the structure or the ambientenvironment, (b) selective heat exchange between the absorber and thestructure or the ambient environment, and (c) an effective means forapplying solar energy or alternate source energy to the absorber. Theseelements of the system are provided, in the preferred embodiment, by thestructural system illustrated in FIGS. 2-9 and described below.

Referring first to FIG. 2, the incorporation of the heat pump system ofthe present invention into a rooftop system, making it particularlyadvantageous for utilizing solar energy and for construction on existingbuildings will be described. The system includes an absorber container31 which contains a vapor absorptive chemical, the vapor pressure andtemperature characteristics of which may be, for example, those definedby line 15 of FIG. 1. This container 31 is situated on the rooftop ofthe building or structure 33 for direct collection of solar energy 35. Asecond container, the vaporizer container 37, is mounted within the roof39 of the structure 33 in the shade of the absorber container 31. Thevaporizer container 37 contains a liquid to be absorbed by the chemicalin the absorber container 31 and may have, for example, the vaporpressure-temperature characteristics defined by line 13 of FIG. 1. Theinteriors of the containers 31 and 37 are interconnected by a conduit 41including a valve 43 for discontinuing or modulating vapor flow betweenthese containers. It will be recognized from the previous descriptionthat vapor will flow through the conduit 41 in either direction,depending upon the operational mode of the system, to provideevaporation in the vaporizer 37 and absorption in the absorber 31, or,alternatively, to provide desportion in the absorber 31 and simultaneouscondensation in the vaporizer 37.

In addition to being subjected to solar radiation 35 the absorbercontainer 31 is subjected to a flow of heat transfer air entering theabsorber 31 from a duct 45 and leaving the absorber 31 through a duct47. The entry duct 45 is connected through an alternate energy sourceheater 49 (such as a natural gas heater) to a two-way valve 51. Thevalve 51, upon actuation, will connect the duct 45 with either ambientair from a conduit 53 forced by a blower 55 or, alternatively, with airfrom the interior 57 of the structure 33 drawn through a conduit 59 by ablower 61. In the solid line position of the valve 51, air from theconduit 59 enters the inlet conduit 45. In the dotted line position ofthe valve 51, air from the conduit 53, that is, ambient air, is blown tothe inlet conduit 45. Thus, the absorber 31 may be subjected,alternately, to heat exchange with an air flow from the house 57 or theambient environment outside of the structure 33, either flow beingoptionally heated, if desired, by the application of heat at the heater49.

The outlet conduit 47 of the absorber 31 carries this heat exchange airalternately to the interior 57 of the structure 33 through conduit 63 orto the external environment through an outlet conduit 65, depending uponthe position of a two-way valve 67. If the valve 67 is in the solid lineposition, air from the outlet conduit 47 will enter the interior 57 ofthe structure 33. If, on the other hand, the valve 67 is in the phantomline position, this air will be exhausted through the conduit 65 to theexternal atmosphere.

The valves 51 and 67 additionally control the flow of heat exchange airpast the vaporizer container 37. The vaporizer 37 includes an inletconduit 69 and an outlet conduit 71 used for manifolding heat exchangeair past the vaporizer container 37. The inlet conduit 69 isalternatively connected to the interior 57 of the structure 33 or theexternal ambient through the conduit 53 by the valve 51, the connectionbeing made to the ambient environment when the valve 51 is in a solidposition and to the interior 57 of the structure 33 when the valve 51 isin the phantom position. In a similar manner, the valve 67 conducts theheat exchange air from the outlet conduit 71 of the vaporizer 37 to theexternal ambient through the conduit 65 when the valve is in its solidposition or to the interior 57 of the structure 33 when the valve 67 isin its dotted line position.

Thus, a simple pair of valves 51 and 67 may be utilized to control allof the heat exchange air utilized for heating and cooling the absorber31 and vaporizer 37. Thus, the valves 51 and 67 control the heatexchange relationships, and are adjusted for seasonal and diurnalcycles. The valves 51 and 67, in a wellknown manner, may beautomatically controlled in response tb the temperature of the structure33 and the ambient environment. Finally, the valve 43 can be adjusted tocontrol the rate of vapor movement between the absorber 31 and thevaporizer 37. In particular, and again utilizing the chart of FIG. 1 incombination with the schematic diagram of FIG. 2, we may first assumethat, during the daytime of summer months, the interior 57 of thestructure 33 is to be refrigerated or cooled. The two-stagerefrigeration process begins with the first stage, described above, byplacing the vaporizer 37 at point 17 and the absorber 31 at point 19 inFIG. 1. During this phase of operation, the valves 51 and 67 are intheir phantom line position, so that air from the interior 57 of thestructure 33 is cooled through circulation past the 32° F. vaporizer 37by the blower 61. At the same time, the absorber 31 is maintained in aheat exchange relationship with the outside ambient atmosphere to keepits temperature at approximately 145° F. at point 19 in FIG. 1. It willbe seen from FIG. 2 that the phantom line position of the valves 51 and67 conducts the outside ambient atmosphere from conduit 53 to theabsorber 31 and returns this air to the outside conduit 65, all drivenby the blower 55. Thus, the simultaneous phantom line positioning of thevalves 51 and 67 permits cooling of the interior 57 of the structure 33during the first stage of the refrigeration cycle. It will be recognizedthat, although solar energy 35 is being absorbed by the absorber 31during this first phase, it is nevertheless possible, by ductingsufficient air from the outside ambient atmosphere through the ducts 45and 47, to maintain the temperature of the absorber 31 at 145° F. asshown at point 19 in FIG. 1. It may be desirable, however, to provide ashutter or a reflective sheet to exclude solar energy 35 from strikingthe absorber 31 during this refrigeration phase.

When during this first stage of refrigeration operation, sufficientwater vapor has passed from the vaporizer container 37 to the absorber31 to saturate the vapor absorptive chemical in the absorber container31, the second stage of operation, a regeneration stage, is begun.During this operational stage, as previously described, the vaporizer 37will be maintained at point 23 of FIG. 1 while the absorber 31 will bemaintained at point 21. This is accomplished by utilizing solar energy35 to raise the temperature of the absorber 31 to 225° F., as shown atpoint 21, so that the vapor pressure within the absorber 31 in this caseis approximately twice the vapor pressure within the vaporizer 37 solong as the vaporizer 37 is maintained at 75° F. This is accomplished byheating the absorber 31 utilizing solar energy while the valves 51 and67 are in their solid line position but while the blower 61 isdeactivated; thus, no air is driven through the conduits 45 and 47 andthe temperature in the absorber 31 is allowed to increase in response tothe solar energy 35. At the same time, ambient air is drawn by theblower 55 through the duct 53 and the inlet conduit 69 to cool thevaporizer 37 so that its temperature is maintained at 75° F. This air isthen discarded to ambient through the conduit 65. Thus, during theregeneration or second stage of the refrigeration or air conditioningprocess, water vapor is desorbed from the vapor absorptive chemical inthe absorber 31 and condenses in the vaporizer 37, heating the vaporizer37, but this heat is liberated to the surrounding ambient air. Once thevapor has been removed from the vapor absorptive chemical, the firststage of the refrigeration process can again commence, cooling theinterior 57 of the structure 33. It will again be recognized that,during the two phases of operation of this refrigeration cycle, anattempt has been made to maintain the vapor pressure differential at2-to-1 in order to assure adequate vapor self-pumping within the system.It should be noted, however, that this 2-to-1 ratio is not necessary andthat if, for example, the ambient temperature is above 75° F., it isnevertheless possible to regenerate the system. So long as the solarenergy is sufficient to raise the temperature of the absorber 31approximately 130° above the ambient temperature, this condition iseasily satisfied on most days which are sufficiently warm to require airconditioning of the structure 33.

If it is now assumed that the house is to be heated on a summer nightafter this refrigeration cycle has ceased, it is possible to terminatethe refrigeration cycle with the vaporizer 37 at point 17. Outsideambient air may now be ducted into a heat transfer relationship with thevaporizer 37 by putting the valves 51 and 67 in the solid line position,so that the vaporizer 37 does not cool below approximately 30° F. At thesame time, air from the interior 57 of the structure 33 is blown by theblower 61 past the absorber 31 which liberates heat at approximately145° to heat the interior 57. It will be recognized, of course, that ifit is possible to maintain the temperature of the vaporizer 37 above 30°F., it will be possible, in turn, to heat the structure 33 at atemperature above 145°. During this operation, the temperature of thevaporizer 37 will be maintained at some point along the line 13 betweenpoints 17 and 23, leading to an absorber temperature between the points19 and 29 on line 15 of FIG. 1.

It will next be assumed that, during the winter, heat is to be storedduring the daytime hours and liberated at night so that the heat pumpacts as a heat storage mechanism for solar energy. During the daytimehours, air is ducted from the interior 57 of the structure 33 past theabsorber 31 and is returned to the interior 57. Solar energy 35 is thuspermitted to heat the house directly during the daytime, while at thesame time storing excess heat in the absorber chemical 31. This isaccomplished by placing the vaporizer 37 in a heat exchange relationshipwith the external ambient air to cool the vaporizer 37, the ambient airbeing directed by valves 51 and 67 in their solid line position. Thevaporizer 37, during this operation, is maintained at point 23 ofFIG. 1. Solar energy is directly applied to heat the air ducted throughthe ducts 45 and 47 and thus to heat the house 57. Any excess heat isutilized to store energy within the heat pump system by desorbing watervapor from the absorber 31, which water vapor condenses in the vaporizer37. On a winter night, when this stored heat is to be utilized, theabsorber 31 is placed in a heat exchange relationship with the interior57 by placing the valves 51 and 67 in their solid line position in FIG.2 and operating the blower 61. At the same time, the vaporizer 37 isplaced in a heat exchange relationship with the outside atmosphere byoperating the blower 55, so that the vaporizer 37 is maintained at point23 while the absorber 31 is maintained at point 29 in FIG. 1. Thevaporizer 37 is maintained at point 23 through its heat exchangerelationship with the outside atmosphere. It will be recognized that,under these conditions, the vaporizer 37 tends to cool, but is warmed bythe ambient atmosphere, while the heated absorber 31 is utilized to heatthe interior 57 of the structure 33. If the outside atmosphere isinsufficient to maintain the vaporizer at point 23 in FIG. 1, thetemperature of the vaporizer 37 will drop and the heating temperature ofthe absorber 31 will in turn drop, but the temperature differentialbetween these members will nevertheless permit the interior 57 to beheated at a temperature which approaches 130° warmer than the outsidetemperature, sufficient on even the coldest winter day to heat theinterior 57.

After an extended period of cloudy skies during which no substantialsolar energy can be collected, it is also possible to utilize thepresent system as a heat pump in combination with the heater 49 of FIG.2 to heat the interior 57 of the structure 33 while using less energythan would be required if the heater 49 were utilized to heat thestructure directly. This is accomplished by utilizing, as in the priormodes, a two-stage, continuous process. The first stage of the processis identical with the cooling stage during refrigeration except that inthis case the vaporizer is located in a heat exchange relationship withthe cold external environment from which it withdraws, on vaporization,thermal energy equivalent to the heat of vaporization of the enclosedchemical. The absorber simultaneously is located in a heat exchangerelationship with the space being warmed and there liberates the heat ofvapor absorption at an elevated temperature. These are accomplished atpoints 17 and 19, respectively, in the chart of FIG. 1, the valves 51and 67 being in the full line position of FIG. 2. In the second stage ofheating, the vaporizer 37 is in a heat exchange relationship with theinterior 57 of the structure 33. This is accomplished by placing thevalves 51 and 67 in the dotted line position, which also places theabsorber in a heat exchange relationship with ambient air pumped by theblower 55 and heated by the heater 49. The absorber is raised to point25 in FIG. 1, causing vapors to desorb from the absorber chemical andmove through the conduit 41 to the vaporizing container 37 where theycondense and liberate heat at point 27 in FIG. 1, this heat being usedfor space heating in the structure 33. The overall result is thatthermal energy is provided to the area being warmed at both stages ofthe chemical heat pump process, and the sum of these energies is greaterthan the energy supplied to the absorber 31 by the heater 49.

FIG. 16 illustrates an alternative arrangement of the heat pump of thisinvention useful for heating the interior 57 when the outside airtemperature is substantially below 50 degrees Farenheit. During theabove-mentioned first heating stage, when the absorber heats theinterior air, it is desirable to pass air from the interior 57 throughthe vaporizer 37 before passing it through the absorber 31. For thispurpose, a blower 61a, valves 51a, 51b, 67a, and the conduit 63a areadded to the structure illustrated in FIG. 1. For normal operation, thevalves 51a, 51b and 67a are disposed in their dotted line positionsillustrated in FIG. 16. When the outside air temperature is very low,air from the interior 57 may be passed through the vaporizer 37 and thenpassed through the absorber 31 by moving the valves 51a, 51b, and 67a totheir solid line positions illustrated in FIG. 16 and activating theblower 61a. The interior air will then be drawn by the blower 61athrough the conduit 63, then through the blower 61a and will then passinto the vaporizer 37. The air then passes from the vaporizer 37 throughthe valve 51b and into the absorber 31. The absorber heats the air,after which the air is returned to the interior 57 through the valve 67aand through the conduit 63a. In this manner, the rate of evaporation inthe vaporizer is maintained at a reasonable level despite very lowoutside temperatures, It may be desirable to supplement the heatingoperation with the heater 49, in which case the blower 59 may beactivated to pass air heated by the heater 49 through the absorber.

Having explained the overall operation of the heat pump system and itsparticular advantages when used as a rooftop system where the absorber31 is directly absorbing solar energy 35, the detailed elements of thesystem and, in particular, the detailed construction of the absorber 31and vaporizer 37, will be described. These elements must be inexpensive(to keep the cost of the overall system at a minimum) while beingextremely efficient, and provide the large heat transfer required forspace heating in structures 33.

FIG. 3 shows a somewhat schematic illustration of the heat pump systemof this invention removed from the structure 33 of FIG. 2 so that thedetailed construction of the various elements and ducting between theabsorber 31 and vaporizer 37 may be better understood. In actuality, theabsorber 31 is comprised of plural identical absorber panels 72 and thevaporizer 37 comprises plural separate vaporizer panels 73. Each of theabsorber panels 72, as previously explained, are supplied with heattransfer air by a lower duct 45, which air is removed by an upper duct47. Similarly, each of the vaporizer panels 73 is supplied with heattransfer air from a first duct 69, which air is removed from the panels73 by a second duct 71. The valves 51 and 67 interconnect the supplyducts 45, 71 and removal ducts 47, 69, respectively, with the ambientair ducts 53 and 65 and structure air ducts 59 and 63, all as also shownin FIG. 2. The absorber panels 72 may conveniently rest directly on theroof of the structure 73 (FIG. 2), so that the duct work as well as thevaporizer panels 73 may be placed in the attic space above the house,but protected from the elements by the structure's roof. In thepreferred embodiment, vapor from each of the absorber panels 72 isinterconnected only with a single vaporizer panel 37, so that multipleabsorber-vaporizer pairs exists, each pair operating as an independentheat pump and each pair being interconnected by a conduit 41 and valve43. It will be appreciated, of course, that if the structure shown inFIG. 3 is to be installed on a flat rooftop or at a location separatedfrom the structure 33 the vaporizer panels 37 should be placed in theshade, so as not to directly absorb solar energy. For this purpose, theabsorber panels 72 may be used to shade the vaporizer panels 73. It willalso be recognized by those familiar with solar collectors that theabsorber panels 72 should be inclined in a southerly direction ifinstalled in the northern hemisphere and should be inclined atapproximately the latitude of the installation location for mostefficient solar collection throughout a normal year.

Referring now to FIGS. 4, 5 and 6, the details of construction of eachof the vaporizer panels 73 will be described, as well as the method ofinterconnecting these panels 73 with the respective ducts 69 and 71.

The panel 73 is made up on an upper insulating layer 81, a lowerinsulating layer 83 and a liquid container 85. The upper insulatinglayer 81 may simply be a rectangular insulating foam pad, while thelower insulating layer 83 is a rectangular insulating frame 86surrounding a thinner insulating web 87 formed integral with but spacedfrom the ends of the frame 85. The container 85 is supported on theinsulating layers 81 and 83 and, in particular, is positioned so that asurrounding lip 89 of the container 85 seats within a recess 91 in theupper insulating layer 81 (as best seen in FIG. 5). Preferrably, thelower surface of the upper insulating member 81 is recessed at 93 sothat air supplied by the duct 69 can flow both above and below thecontainer 85, the upper flow being through the recess 93 and the lowerflow being through a space 95 between the thin web 87 and the lowerportion of the pan 85. Thus, the pan 85 is totally suspended between theinsulating layers 81 and 83 with air flow from the duct 69, which isalso made from insulating material walls 97, completely enveloping thepan 85 for maximum heat transfer.

The pan 85 is a relatively thin, large, flat container being, in apreferred example, 12 inches by 65 inches in plan and 1 inch thick. Aliquid to be vaporized, such as water 99, partially fills the container85. The container 85 is preferrably constructed as a very shallow flatpan having a thin metal foil bottom 101 and thin metal foil top 103made, for example, of tin plated steel or aluminum. It will berecognized, that, for maximum efficiency, as with other evaporativerefrigeration systems, a vacuum must be maintained within the container85. The thin metal foil walls 103 and 101 will not support atmosphericpressure once the container 85 is evacuated, and for this reason pluralribs 107 of metal or plastic are positioned between the upper and lowerwalls 101, 103, to keep them separated when the container 85 isevacuated. As particularly shown in FIG. 6, the webs 107 may preferablybe discontinuous, leaving a central manifolding portion 109 within thecontainer 85 for supplying vapor to and from each of the intersticiesbetween the respective webs 107.

In the preferred example, the walls 101 and 103 are formed of 11-millsteel plated with tin, an extremely inexpensive, thin-walled structurebeing formed from this material.

To improve thermal conductivity within the vaporizer containers, theinner surfaces may be covered with capillary material, such as porouspaper. This results in a heat pipe effect, with the vapors freely movingthrough the open space between the container walls and condensing orevaporating at the walls, while liquid is automatically distributedthrough the walls by capillary movements. As a consequence of theseactions, the entire vaporizer approaches a constant temperaturethroughout its structure.

Centrally located, and in communication with the container 85, is ademisting device 109 which, in the preferred example, includes pluralstacked, spaced, centrally apertured washer members 111 separated byplural stacked discs 113, all supported, for example, on a central rod115. The diameter of the discs 113 is greater than the inside diameterof the washers 111. Vapor passing through the demisting device 109 mustpass through the labyrinth formed by the members 113 and 111, which may,for example, be formed of filter paper. This labyrinth tends to removeany liquid droplets from the vapor so that the vapor reaching theconduit 41 after evaporation in the container 85 will be free of liquiddroplets. It has been found that liquid droplets deteriorate the vaporabsorbant chemical in the absorber trays 72, and the demister 109 istherefore helpful in assuring that only pure water vapor reaches thevapor absorbant chemical. The entire demister 109 is housed within acylindrical cavity 117 which passes through the upper insulating pad 81and upper wall 103, and is connected to an enlarged end 119 of the vaporconduit 41.

It will be understood that the remaining duct 71 interconnects with theother end of the panel 73 in a manner similar to that shown for the duct69 in FIG. 5, so that high volume air flow surrounding the entirecontainer 85 is permitted by the ducting at each end. Heat can,therefore, be very efficiently transferred from the container 85 throughits thin metal walls 101, 103 into the air flow in the thin passages 93and 95 to form an effective heat transfer between the air from the duct69 and the water 99 within the container 85.

An alternative embodiment of the vaporizer container is illustrated inFIG. 14. The unit shown in FIG. 14 consists of four glass tubes 600,preferably in the form of fluorescent light tubes. Surrounding the tubesis a manifold 6l0, preferably formed from an inexpensive light plasticmaterial which forms an air space 620 between the tube 600 and themanifold 610. The interior portion 630 of each tube 600 is terminated inanother manifold 640 having vapor conduit 660 attached to the manifold640. Each air manifold 610 is terminated in the manifolds 670 and 1000.In this embodiment of the vaporizer container, the tubes 600, as bestshown in FIG. 15, contain the water or ice to be vaporized or sublimatedfor transfer into the absorber panel through the vapor conduit 660. Heatexchange is accomplished through air which moves through the manifoldformed by the structure 670 and through the air passage 620, where theair contacts the surface of the glass tube 600 and transfers heat fromor to the water inside the tube interior 630 through a capillarymaterial 1001. Because the liquid in the vaporizer vaporizes orcondenses spontaneously, and the speed of such a process affects thetotal operation of the chemical heat pump, it is advantageous to attacha capillary material to its interior wall. The capillary material causesliquid which otherwise would accumulate at the bottom of the tube duringvaporization, to become distributed over the entire surface of the tube,thereby increasing the efficiency with which the heat exchange iseffected. Likewise in vapor condensation, the liquid does not accumulatein droplets, but distributes itself as a film, as well as a puddle inthe bottom, which has improved thermal conductivity. I have found thatglass cloth, denoted as 1001 in FIG. 15, is an excellent capillarymaterial. One means of attaching the cloth 1001 to the interior of thetube 600 is a silicon resin used as an adhesive. Another method ofattaching the cloth 1001 to the tube 600 is to place a polypropylenescreen against the interior surface 1002 of the cloth 1001. Because theabsorber contains magnesium chloride, the vapor which cycles in and outof the absorber may, at times, contain enough hydrogen chloride to formaqueous hydrochloric acid in the vaporizer in sufficient concentrationto etch materials subject to attack by hydrochloric acid. Use of theneon or fluorescent light glass tubes of this embodiment eliminates thisproblem since glass is impervious to etching by hydrochloric acid.Furthermore, such tubes may be obtained cheaply, thereby reducing costsin fabricating the vaporizer container. Furthermore, such tubes areoften operated with a reduced pressure in the interior and, in any case,do not require structural support for the glass. Thus, the support ribs107, illustrated in FIGS. 5 and 6, may be eliminated and are notnecessary in this alternate embodiment of the vaporizer container,further reducing cost of fabricating the vaporizer container of thisalternative embodiment. From the illustration in FIG. 15, it is seenthat the water in liquid form is intended to rest on the bottom of thetube 600. Therefore, the vaporizer container in FIG. 14 is preferablyoriented such that the tubes have their axis of symmetry disposedhorizontally level. It is important to note that the air manifold 670 isconnected to the heat exchange air control system in the same mannerthat the passage 69 of the vaporizer container in FIG. 5 is connected.Also, the conduit 660 is connected to the absorber panel in the same waythat the passage 41 of the vaporizer container illustrated in FIG. 5 isconnected to the absorber panel.

Turning now to FIGS. 7, 8 and 9, the details of construction of theabsorber panels 72 will be described. The panels are shown mounted onplural T-channels 121 which may, for example, be supported on the roofof the structure 33 (FIG. 2). These T-channels 21 in turn support metalbrackets 123 which form lower supports for a pair of resilient supportframes 125 formed, for example, of an insulating polymer material. Thesesupport frames 125 are used to support plural transparent covers 127,129 and 131. The covers 127-131 may be, for example, glass sheets whichare used in the manner typically employed in flat plate collectors toallow the absorption of solar energy while protecting the system fromexcess reradiation or convection of absorbed energy.

The channels 121 additionally support a lower insulating cover 133 whichforms a lower support for a vapor absorptive chemical container 135. Thecontainer 135 is preferrably formed as a shallow pan similar to the pan85 used for the vaporizer container 85. In the illustrative example,described above, the pan 135 typically has dimensions of 36 inches by 84inches in plan and a thickness of 1/2 inch. The pan 135 preferrablyincludes a flat lower wall 137 resting on the insulating pad 133 and acorrugated upper wall 139 spaced from the lowest glass plate 127. Thecorrugated upper surface 139 increases the surface area for heatconduction from an enclosed chemical 141 such as a magnesium chloridehydrate to the air space 141 separating the top panel 135 from the glasslayer 127. The air space 141 is extremely important since it forms theflow channel for air entering the absorber panel 72 from the duct 45 andinterconnects the duct 45 to the duct 47 (FIG. 2). As shown in FIG. 9,the duct 45 is insulated, as is the duct 47. The pan 135 preferably isshorter than the insulating lower cover 133 so that it can form anopening 145 for communication with air space 143. Thus, the conduit 45freely communicates with the entire end of the air space 143 and a lowvelocity, low eddy flow of air is pumped from the duct 45 through theair space 143. This flow is less efficient than a turbulant flow inexchanging heat between the air flow and the vapor absorptive chemical141, but the available surface area is so great that this is nodetriment. It has been found to be extremely effective in loweringconvection losses between the container 135 and the ambient atmosphereabove the glass plate 131, and is an important feature of thedisclosure.

The container 135 is evacuated, as was the container 85, and is thussubjected to atmospheric pressure outside of the container. In thisinstance, the chemical 141 is held against the corrugated upper wall 135by a corrugated or zig-zag shaped, vapor permeable partition 147conforming to the corrugations or zig-zags in the upper wall 139. Thisforms a zig-zagged layer, as shown in FIG. 7, of absorptive chemical141, greatly increasing not only the surface area for heat transfer butalso the surface area for vapor transfer between the chemical 141 andthe vapor space 149 between the partition 147 and lower wall 137. Insome cases, the zig-zag structure is not needed. This vapor space 149communicates with the vapor conduit 41 (FIG. 9). In this regard, pluralpartitions 151 and 153 used for supporting, respectively, the upper andlower ridges of the zig-zagged partition 147, terminate short of thecenter of the panel 72, as shown in FIG. 9, to form a central manifold155 for conducting vapor to the vapor conduit 41.

The vapor absorptive chemical container 135 is thus available for directheat exchange with the air flowing in the space 143 and is available forvapor transfer through the vapor permeable partition 147. This partition147 may conveniently be formed, for example, from filter paper folded ina corrugated fashion. The lower wall 137 of the absorber container 135is typically constructed from light gauge steel or aluminum, while theupper wall 139 is made of extremely thin sheet metal or foil material,such as 3 mill aluminum, which is tightly pressed against the absorbantchemical 141. This assures that, as the absorbant chemical 141 expandsand contracts during vapor absorption and desorption, respectively, thewall 139 moves with the surface of the chemical 141 so that voids arenot formed between these layers which would interfere with efficientheat transfer. Thus, the partitions 151 and 153 support the upper wall135 by forcing the chemica1 141 against the wall 135, rather thanindependently supporting the wall 135, so that voids are eliminatedduring repeated usage cycles.

While the absorber 31, shown in FIGS. 2, 3, 7, 8, and 9 is satisfactoryfor some purposes, the collector design shown in Figures 1O and 11 hasbeen found to be a much more efficient solar collector, primarily sinceits ability to retain heat once collected is greatly enhanced. It shouldbe understood that the solar collector of FIGS. 10 and 11 is designedfor mounting on the rooftop of the structure 33 in FIG. 2 in place ofthe absorber 31. Like the absorber panels 72 of the absorber 31 shown inFIG. 3, the absorber of FIGS. 10 and 11 will, in many instances, takethe form of multiple absorber panels each independently connected to avaporizer 37. It will also be understood from the following descriptionthat the solar collector of FIGS. 10 and 11 is designed for connectionbetween the air ducts 45 and 47 of FIG. 3 and for connection to a vaporconduit 41 in a manner identical to that described for the absorberpanel 72.

The improved solar collection panel includes an outer frame 161providing a flat, lower wall 163 and surrounding side walls 165, theside walls 165 serving to support the various layers of the collector bymeans of plural grooves 167. It will be understood, of course, that anyconvenient mounting hardware may be utilized to support the variouslayers of the collector, one above the other, in the manner to bedescribed below. The grooves 167 have been found convenient for thispurpose, however, and it will be understood that in those instanceswhere certain layers of the apparatus are to be evacuated, the walls ofthese layers will be sealed within the grooves 167.

An insulating layer 169 rests against the flat, bottom wall 163 toinsulate the remaining portions of the solar collector from the roof 39(FIG. 2) of the supporting structure. Seated directly on top of theinsulating layer 169 is the vaporizer container 171 which includes upperand lower thin foil walls 173 and 175, respectively, sealed together attheir perimeters and enclosing a layer of vapor absorptive chemical 177situated adjacent the upper foil wall 173. The upper surface of the wall173 is coated with material that imparts high solar radiant energyabsorption and low infrared emissions, typically a ratio of about 4.Such coatings are presently available. The vapor absorptive chemical 177is supported by a vapor permeable wall such as a filter paper wall 179which is, in turn, supported by plural ribs 181 in a manner similar tothat described previously. The ribs 181 are intended to support thevapor absorptive chemical 177 even though the container 171 isevacuated, thus leaving a vapor manifolding space 183 between the ribs181. As in the absorber described previously, the ribs 181 are separatedto form a manifolding channel 185, as shown in FIG. 10, and thismanifolding channel may be used to support a vapor tube 187 which isconnected, in turn (in a manner not shown in FIGS. 10 and 11), to thevapor conduit 41. The tube 187 may conveniently be perforated inalignment with the openings between adjacent ribs 181 to equalize theflow of vapor throughout the collector mechanism.

As in the previous embodiment, the container 171 is sealed and evacuatedand thus the upper wall 173 and lower wall 175 are crimped together at189 to form a closed vapor system.

In the prior embodiment air from the house or the ambient was drawndirectly over the absorptive chemical container during both daytime andnighttime use. In the embodiment of FIGS. 10 and 11, however, it hasbeen found that, because of the extremely high temperatures which can beexpected during the daytime at the upper wall 173 of the container 171,it is virtually impossible to maintain eddy-free flow in the space 191of the container 171. Such eddy currents induce turbulence in the flowwhich can substantially increase the thermal loss from the container 171to ambient. For that reason, the embodiment shown in FIGS. 10 and 11,although it conducts nighttime air to the space 191, does not utilizethis space for the passage of daytime air for solar heating of thestructure, but rather uses an alternate flow passage which will bedescribed below.

In addition to bypassing daytime air flow around the channel 191, acellular or honeycomb structure 193 is placed in the air space 191. Ithas been found that this cellular structure 193 can be used to avoidstrong eddy currents, and thus losses due to eddy currents can besubstantially reduced. The honeycomb structure 193 is preferablyconstructed of transparent or reflective sheets arranged perpendicularto the absorber surface so that sunlight reflected from the surfacescontinues toward the absorber. The sheets are advantageously very thinto minimize the conduction of heat by the sheets themselves. Reflectivecoatings appear to be attractive because reflecting surfaces have lowemissivities in the infrared range whereas materials transparent tosunlight tend to introduce large thermal radiation losses.

To illustrate the spacing requirements for a cellular construction, ithas been found that where the tilt of the overall roof and its solarcollector is 45 degrees, where the wall 173 of the container 171 issolar heated at a temperature of 300° F., and where the firsttransparent collector plate 195 is at 100° F., a spacing of 0.33 inchesis required for the honeycomb structure 193 in order to eliminate strongeddy currents. During such daytime conditions, even though no forcedflow exists in the channel 191, the honeycomb panel 193 greatly reducesthe convection losses from the system and thus enables the system tomaintain high solar absorption temperatures.

The air space 191 is enclosed by the first collector cover 195,typically formed of glass or other transparent material. This cover 195may be used to support the honeycomb structure 193 which is attachedthereto, as by adhesive.

The cover 195 and the next adjacent cover 197, which is also formed oftransparent material such as glass, together form a daytime air flowchannel 199. This channel 199 is open to the duct 45 (since the glass195 includes an opening 201 above the duct 45). It will be understood,in addition, that the glass cover 195 includes a similar opening at theother end of the solar collector for communication with the duct 47.

In order to reduce thermal radiation losses to the clear night skyduring nighttime operation of the collector of FIGS. 10 and 11, orduring operation of the system in the cooling mode, a reflective sheet203 is designed to be selectively placed between the upper wall 173 ofthe container 171 and the lower side of the honeycomb partition 193.This reflective sheet 203 may be conveniently stored during daytimeoperation on a roller 205 which is rotationally spring biased in thesame manner as is used for common night shades in houses. A valvingmechanism 207 rotates about the same axis as does the sheet roller 205and includes a flexible sealing member 209 which seals along one edgeagainst the inlet conduit 45 and along its opposite edge against theroller 205. In the position shown in FIG. 11, the valve mechanism 207forces air which enters the system from the conduit 45 to pass throughthe space 191 exclusively. This position is utilized for nighttimeoperation, and it will be noted that at night the sheet 203 forms theupper wall of the air flow passage 191. The sheet 203 fits into groovesin the sides 165 of the overall container and thus seals this air flowpassage so that the honeycomb structure 193 does not impede normal airflow. The sheet 203 also permits a relatively thin air flow passageduring nighttime operation, while at the same time permitting the airspace 191 to be relatively wide to accommodate the honeycomb baffles 193during daytime operation. Plural cords 211 may be used to selectivelydraw the sheet 203 between the elements 173 and 193 at dusk fornighttime use.

It has also been found that convection losses may be kept low byreducing the pressure between the second transparent cover 197 and afinal third transparent cover 203. The cover 203 is formed oftransparent material, such as glass, as were the covers 197 and 195. Thespace between the covers 197 and 203, however, is advantageouslypartially evacuated in order to reduce convection losses. The forceswhich are generated by the atmosphere once this space has been evacuatedmay be supported by plural, short, cylindrical spacers 213, each formedof thin wall material, such as metal sheet, and each being madereflective so as not to interfere with the absorption of sunlight by thecontainer 171. One wall of each of the cylinders 213 is advantageouslyapertured to assure that no pressure differential exists across thecylindrical walls. It has been found that by using these cylinders 213,the pressure within the space between the covers 197 and 203 can bereduced to a level below 245 torr to substantially suppress free eddyformation within this air space and thus reduce the convection losses.

In order to maintain the vacuum between the covers 197 and 203, asealing member 215 is inserted in a groove in the side wall 165 to sealthe perimeters of these covers 197,203.

During daytime use of the solar collector of FIGS. 10 and 11, the valvestructure 207 is rotated to force air pumped into the system to flowalong the dotted line path between the covers 195 and 197. It has beenfound that sufficient heat will flow from the absorptive chemicalcontainer 171 to this air space to heat the air for winter daytime spaceheating purposes. At the same time, the air flow through this air spacecan be maintained relatively free of eddies, since one wall is not sohot as to form eddy currents (as would be the case if the air was passedthrough the space 191). This air flow through this air space duringdaytime usage substantially reduces the convection losses during thedaytime to the atmosphere. In order to maintain laminar flowcharacteristics, the Rayleigh number must be kept below its criticalvalue along the flow path. Since the Rayleigh number changes as the airis heated, it has been found advantageous to make the air space 217between the covers 195 and 197 taper so that, in a typical example, atthe inlet adjacent the conduit 45, this air space may have a thicknessof 0.21 inches, whereas at the outlet adjacent the conduit 47, thethickness may be 0.44 inches. The passage 217 is thus maintained as thinas possible to permit substantial heating of the air passing through thesystem during winter daytime usage, but is nevertheless maintained wideenough to assure low eddy flow at each location. This requires thetapering of the flow channel 217 for most effective operation.

The solar collector of FIGS. 10 and 11 substantially increases theefficiency of the overall solar system by reducing daytime convectionand nighttime radiation losses from the system through the use of thehoneycomb structure 193, the sheet 203, and the pair of air flowpassages 191 and 217 for alternate daytime and nighttime use. Theevacuated air space utilizing the supports 213 between the flat plates197 and 203 further reduces convection losses. The overall effect ofthese loss reduction features is to make the system operate moresatisfactorily for year-around heating and cooling purposes.

It will be understood that the wall 173 of the container 171 and thepartition 179 may each be corrugated as was shown in the embodiment ofFIG. 7 to increase the surface area available for heat transfer andsolar radiation absorption. It will also be understood that the uppersurface of the wall 173 may be blackened or otherwise treated to inhanceits solar absorption qualities. In this embodiment, as with the previousembodiment, the wall 179 of the container 171 is maintained thin enoughto follow the contraction and expansion of the chemical 177 duringdesorption and absorption of vapors, so that spaces are not formedbetween the chemical 177 and the wall 173 which would inhibit heattransfer.

FIGS. 12 and 13 illustrate an improved version of the alternativeembodiment of the absorber panel illustrated in FIG. 10. This improvedversion is an absorber for a chemical heat pump system with featuresthat offer excellent performance with a relatively simple geometry. Anabsorbent chemical 480 is held in a tray 490 over which is placed asolar absorbing vapor permeable screen 470 forming the vapor manifoldingspace 550 with a glass panel 430. The glass panel 430 and the tray 490form an evacuated container. A glass panel 420 forms a passage 450 fordaytime air with the lower glass panel 430. The container 490 forms anighttime air passage 500 with the surface 510 of an underlyinginsulator 520. A top glass panel 410 forms a space 440 for inert airwith the lower glass panel 420. The improved embodiment alsoincorporates a valve 530 moved about a hinge 540 for controlling thepassage of daytime and nighttime air.

The vapor permeable wall 470 is disposed on the sunlit side of thechemical absorber 480. In the embodiment illustrated in FIG. 12, thevapor permeable wall 470 takes the form of glass cloth. This glass clothalso serves the additional purpose of acting as a solar absorber.

The glass cloth is preferably coated with a coating which readilyabsorbs solar radiation and has a low emissivity for infrared radiation.Such coatings are well known in the art. Also, the screen may preferablybe coated with coatings which have high absorption to substantially allsolar radiation and low emissivity to infrared radiation. Thus, thesurface of the panel 173 of FIG. 11 is eliminated in the improvedembodiment illustrated in FIG. 12 since this function is now combinedwith the vapor permeable screen 470 in FIG. 12 in the improvedembodiment.

In the embodiment illustrated in FIG. 11, the vapor manifolding space183, held at a pressure below atmospheric pressure, was located on theshaded side of the chemical container. In the improved embodiment,illustrated in FIG. 12, the corresponding vapor manifolding space 550 islocated on the sunlit side of the chemical absorber 480. This eliminatesthe need for the additional evacuated chamber of the previous embodimentdefined by the panels 203 and 197 in FIG. 11. Thus, the partiallyevacuated vapor manifolding space 550 of the improved embodiment servesa dual purpose of conducting vapor to and from the absorber chemical 480and as a heat insulator between the chemical absorber 480 and theatmosphere. It further serves to insulate the air passing through thepassage 450 from the heat stored in the absorber chemical 480. Theembodiment illustrated in FIG. 11 uses a honeycomb structure 193 to cutheat losses due to convection caused by the high temperature of theabsorber chemical. The honeycomb structure is not necessary in theimproved embodiment, illustrated in FIG. 12, because the vapormanifolding space 550 serves to insulate the air passage 450 from theabsorber chemical 480. Thus, the improvement illustrated in FIGS. 12 and13 has resulted in the elimination of several expensive parts includingthe evacuated chamber of the previous embodiment, illustrated in FIG. 11between the panels 203 and 197, the cylindrical structural supports 213,necessary to support the panels 197 and 203 against atmosphericpressure, and the honeycomb structure, illustrated in FIG. 11 at 193.Also, the function of the vapor permeable wall and solar absorber havebeen combined into one member, namely the vapor permeable solarabsorbing screen 470 of FIG. 12. The vapor distribution features of thisimproved embodiment are best illustrated in FIG. 13 and consist of aconduit 560 having holes 570 disposed within the vapor manifolding space550. Plural partitions 555 ensure uniform distribution of vapor withinthe vapor manifolding space 550. The improved version of the absorberpanel illustrated in FIGS. 12 and 13 represents a cost savings in thefabrication of absorber panels because of the parts eliminated in thisimproved embodiment as enumerated above.

The functional operation of the improved version of the absorber panel,illustrated in FIGS. 12 and 13, is virtually identical with thefunctional operation of the alternative embodiment absorber panel,illustrated in FIGS. 10 and 11. Vapor from a vaporizer container passesinto the vapor conduit 560 and is distributed to holes 570 and guided bypartitions 555 to be uniformly absorbed by the chemical 480. The dashedline position of the valve 530 illustrates the daytime operating mode ofthe absorber panel of FIG. 12. Heat exchange air is forced through thepassage 455 into the daytime air passage 450 where the air is insulatedeffectively by the vapor manifold channel 550 from the absorbentchemical 480. Eddy currents are thus reduced, thereby cutting convectionlosses due to the heating of the daytime air in the passage 450. Fornighttime operation, the valve 530 is rotated to the solid lineposition, illustrated in FIG. 12, and a screen 580 may be drawn from aspool 590 and disposed over the absorber chemical 480. The screen 580serves to reduce heat losses due to emission radiation from the absorberchemical container 480. In the nighttime operation, the heat exchangeair is passed through the nighttime air passage 500 directly below theabsorbent chemical container 480.

In summary, the upper panel 410 of the absorber container is transparentin order to permit solar radiation to fall directly on the absorberchemical 480. The evacuated space 550 between the glass 430 and the bedof absorber chemicals 480 permits the flow of water vapor to all partsof the chemical bed and also provides good thermal insulation reducingconvective heat losses from the absorber. The low pressure and low flowvelocity in the space 450 lead to a layer of laminar flow without theformation of eddies in the air flow. It provides very effectiveinsulation without the need for a closely spaced honeycomb structure. Acombination of the glass plate 430 as part of the absorber structurealso reduces the number of additional cover plates required andsimplifies the overall collector design. The space 450 next to the vapormanifold passage 550 is used as an air passage during the day.Preferably, air enters from the house at 70° F. and is warmed to 100° F.before returning to the house to be heated. Conditions are selected sothat the air flow is laminar within the space 450 and with minimumeddies and so that the net heating to the house is 1000 BTU per day foreach square foot of collector area on the absorbing screen 470. This isdone by properly choosing the air flow rate, the dimensions of the airpassage 450, and the thickness of the insulating layer formed by thevapor manifold passage 550. The top air space 440 acts as additionalinsulation. Eddies in the air flow would otherwise form in the space 450and add to the heat loss. At night, an alternate air passage 515 is usedon the otherwise shaded side of the absorber in order to maintain thedesired heat rate for the house during conditions with a reducedabsorber temperature. The passage 515 is selected for the nighttime airflow because it is immediately adjacent the absorber chemical 480,thereby maximizing the heat transfer between the air passage and theabsorber chemical 480.

The overall system design shown in FIGS. 2 and 3 provides an extremelyefficient heat pump system which may be used for space heating andcooling, as in structures, according to the vapor pressure-temperaturechart shown in FIG. 1. The use of a low eddy air flow above the absorbercontainer greatly reduces convection losses when solar energy is used asthe source of energy for the heat pump system. In addition, the thin(corrugated) upper wall 139 (173) in the absorptive chemical container135 (171) which allows this upper wall 139 (173) to move with theexpanding and contracting chemical 141 (177) is extremely important inmaintaining high efficiency operation over prolonged cyclical use.

The overall system of the present inventron allows extremely simplecontrol of a pair of valves to operate the entire system for heating andcooling the house during the various seasonal changes, and also allowsoperation of the alternate energy source heater 49 while increasing itseffectiveness based on heat pump principles, without greatly increasingthe cost of the system.

The valve 43, which controls vapor flow through the conduit 41 (FIGS. 2,3, and 9), is an important control element in the system of the presentinvention. Thus, during nighttime heating of house air, the valve 43 canbe adjusted to maintain the temperature of the absorber 31 atapproximately 120° F. and, at the same time, maintain pressures withinthe system low enough to prevent formation of higher hydrates. Duringdaytime use, the valve 43 is typically opened completely to allowefficient regeneration of the system. Between daytime and nighttime usethe valve 43 may be closed when a storage of energy is to beaccomplished. Thus, the control system which is utilized with thissystem should be effective not only to operate the valves 51 and 67, butalso to control the valve 43 for most efficient operation.

What is claimed is:
 1. A solar collector, comprising:a surface forabsorbing solar radiations; a pair of spaced transparent covers mountedover said absorbing surface, said solar radiation passing through saidcovers to impinge upon said absorbing surface, said pair of spaced,transparent covers forming a tapered heat exchange fluid duct, said ductbeing tapered sufficiently to maintain low thermal eddy current flow insaid heat exchange fluid as the temperature thereof increases in passingthrough said duct while still maintaining said duct sufficiently thin toassure substantial heat transfer to said heat exchange fluid, means foralternately ducting heat exchange fluid between one of said pair ofspaced, transparent covers and said surface; and a reflective screenselectively positionable between said one of said pair of spaced,transparent covers and said surface, said screen reflecting radiantthermal energy when said heat exchange fluid is ducted between said oneof said spaced, transparent covers and said surface, said screen, whenpositioned between one of said pair of spaced, transparent covers andsaid surface, defines one side of a flow channel for conducting saidheat exchange fluid.